U.S. Measles Elimination Status at Risk as Outbreaks Spread to 45 States

Since January 2025, when an outbreak began in Texas, measles has not stopped moving through the United States. It has now reached 45 states. A new analysis in The Lancet, from researchers at Boston Children's Hospital, asks whether the country can still claim to have eliminated the disease, a status declared in 2000.

The team is led by Maimuna Majumder, Ph.D., MPH, the Inaugural Peter Szolovits Distinguished Scholar in the Computational Health Informatics Program at Boston Children's. She worked with postdoctoral research fellow Anne Bischops, MD, a pediatrician and German National Academy of Sciences Leopoldina Fellow. They measured the country against the seven indicators the CDC set up after 2000 to keep elimination on track. They looked at case counts, outbreaks, where infections originated, and how readily the virus spreads. The U.S. met all of those indicators when it was last recertified, in 2011. This time, four of the seven are missed outright and the other three are at risk.

The first missed indicator is case volume. The cutoff is fewer than one case per 10 million people, and as of early 2026 the U.S. stood at about 93 per 10 million. The second concerns origin. Most cases should be imported from abroad, but since the start of 2025 only 6 to 7 percent have been, which means the large majority are spreading from within the country.

The third is the number and size of outbreaks. The benchmark is roughly four outbreaks, each of no more than about six cases. Last year the U.S. had 48 outbreaks that produced more than 2,000 cases. In early 2026, at least 19 outbreaks had already produced more than 1,600. The fourth is the transmission rate. Each infected person should pass measles to fewer than one other person on average, and the U.S. exceeded that level more than 75 percent of the time since early 2025.

The three at-risk indicators are, in some ways, the more telling ones. The country is supposed to be able to reach four weeks in which all infections come from outside it, but since the first case in January 2025 it has not managed four weeks without infections acquired domestically, and about 90 percent of cases were acquired here. Herd immunity generally requires about 95 percent of people to have two doses of the measles vaccine, usually given as MMR. Average kindergarten coverage in the 2024-2025 school year was 92 percent. In Texas, the team's earlier work found rates ranging as low as 79 to 90 percent. The last indicator is that cases should not share a single viral strain. Preliminary genetic data show most current cases share one strain and probably belong to the same transmission chain.

Bischops said falling vaccination rates were already a warning sign that measles could return, but that losing elimination status would be a clear and very concerning marker. Majumder stressed that measles is not benign. Even after an infection clears, she said, it can cause lifelong problems. Babies under a year old face the greatest risk of severe complications, and the full effect on children exposed during this outbreak may not appear for years. The researchers argue the findings strengthen the case for vaccinating children from a young age.

The analysis is meant as an early warning ahead of a November 2026 meeting of the Pan American Health Organization's expert panel, which will reevaluate the U.S.'s elimination status.